1. Field of the Invention
This invention relates generally to signalling the load that the load voltage is in regulation. In particular, this invention signals the load that there is a power outage and guarantees sufficient power for an orderly shutdown. The load is a digital computing system and the signal is a logic level which causes a priority interrupt.
2. Description of the Prior Art
Most electronic devices operate from an AC power source of either 110 volts and 60 hertz, or 220 volts and 50 hertz. It is often the case that these electronic devices must in turn produce a constant low-level DC power. This is most often accomplished by an internal power supply which first converts the AC power to a high-level voltage which is subsequently converted to a lower level voltage.
The conversion from high-level DC voltage to low level DC voltage is often accomplished by applying the higher level DC voltage to the primary winding of a step-down transformer. The application of high-level DC voltage is moreover usually accomplished at a high frequency so as to cut down on the size and weight of the step-down transformer. Such a high frequency application to the relatively small transformer core can result in magnetic saturation unless the magnetic energy in the core is released by an opposite or cancelling flux. This is usually accomplished by closely regulating the high frequency application of the DC voltage level so as to allow for the subsequent cancellation of the magnetic flux build-up prior to saturation.
The prior art has the problem that in the event of an overcurrent condition, the main power transformer goes into saturation with ensuing collector current spikes of the switching transistors. These spikes degrade the switching transistor life.
Also, the prior art monitors the AC line voltage and trips a one-shot if there is a voltage outage. Such prior art systems attempt to monitor an AC power outage at the AC input. Such systems are susceptible to minor fluctuations in AC line voltage so as to thereby result in frequent shutdowns. This has somewhat been alleviated by providing one-shot cycles which provide for an orderly shutdown only if the AC line voltage is still out at the end of the one-shot cycle. These systems nonetheless trigger premature shutdowns which may not be yet necessary at the various critical load points wherein power is being supplied.